The development of potassium-ion batteries (KlBs) are hampered by the lack of appropriate electrode materials allowing for the reversible insertion/de-insertion of the large K-ion. Iodine, as a conversion type cathode for rechargeable batteries, has high theoretical capacity and excellent electrochemical reversibility, making it a potential cathode material for KlBs. However, due to the defects of iodine with the poor electronic conductivity and easy dissolution in the electrolyte, an intensive quest for iodine based KlBs enabling high-performance potassium-ion storage is still underway. In this work, a high efficiency capacitive K-I-2 battery has been successfully achieved by constructing a nanocomposite of iodine encapsulated in mesoporous carbon (CMK-3). The as-prepared CMK-3/iodine nanocomposite exhibites excellent rate performance (89.3 mA h g(-1) at 0.5 A g(-1)) and superior cycling stability, which remarkably exceeds most of reported KlBs cathode materials. Such a excellent electrochemical performance can be ascribed to the engineered structure of CMK-3/iodine hybridized electrode which can alleviate the impact of the shuttle phenomenon, improve electronic conductivity and facilitate ion diffusion. As a consequence, iodine within the conductive protecting CMK-3 can afford an extraordinary pseudo capacitive potassium-ion storage, which sheds light on the development prospect of conversion-type electrode materials to meet urgent demand for advanced KIBs. (C) 2019 Elsevier Inc. All rights reserved.